The invention relates to the spray coating of sheet material and, in particular, to the collection of an overspray occurring during such spray coating.
It is conventional to spray coat sheet material for various purposes, for example, it is common to spray paint a vinyl sheet material for us in the automotive industry. One known coating apparatus involves a spray booth through which the sheet travels in a horizontal direction. Disposed in the booth is a rotary sprayer which comprises a rotary nozzle carrier mounted for rotation about a vertical axis. A number of downwardly directed spray nozzles are mounted in a circular pattern on the support to spray the upper surface of the carrier as it rotates and the sheet passes therebeneath.
The circular pattern in which the nozzles are arranged has a diameter larger than the width of the sheet, so that the nozzles cyclically pass into and out of overlying relationship to the sheet. Since it is only necessary for each nozzle to spray during the period in which it overlies the sheet, the nozzles are activated as they sequentially reach one edge of the sheet and deactivated as they leave the opposite edge of the sheet. In order to ensure that both edge regions of the sheet are properly coated, it is desirable to regulate the ON-OFF cycle of each nozzle such that each nozzle oversprays at both of the edges of the sheet, i.e., such that a portion of the nozzle spray pattern extends outwardly past both respective edges of the sheet. The oversprayed coating material must be collected. Heretofore, for this purpose, collector sheets, also formed of vinyl, are placed beneath the edges of the sheet being spray coated. Those collector sheets collect the overspray. At the end of the spray operation, the collector sheets must be disposed of as hazardous waste.
Not only does the disposal of the collector sheets present a problem, due to the presence of the toxic coating material thereon, but difficulties have occurred during the spraying operation itself. In that regard, the spray material may contain solvents which evaporate within the booth. For example, a typical vinyl paint contains keystones (i.e., MEK MAK, MIBK) which vaporizes at 40.degree. F. Such evaporation of solvent produces a vapor-rich environment within the booth which not only poses a hazard to operating personnel, but also may result in the recondensing of solvent onto the sheet, thereby diminishing the uniformity of the applied coating.
Therefore, it is customary to attempt to control the spraying as much as possible to reduce the amount of overspray. Notwithstanding those efforts, however, the above-described problems have persisted.